tcp-full.cc

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/* -*-  Mode:C++; c-basic-offset:8; tab-width:8; indent-tabs-mode:t -*- */

/*
 * Copyright (c) Intel Corporation 2001. All rights reserved.
 *
 * License is granted to copy, to use, and to make and to use derivative
 * works for research and evaluation purposes, provided that Intel is
 * acknowledged in all documentation pertaining to any such copy or 
 * derivative work. Intel grants no other licenses expressed or
 * implied. The Intel trade name should not be used in any advertising
 * without its written permission. 
 *
 * INTEL CORPORATION MAKES NO REPRESENTATIONS CONCERNING EITHER THE
 * MERCHANTABILITY OF THIS SOFTWARE OR THE SUITABILITY OF THIS SOFTWARE
 * FOR ANY PARTICULAR PURPOSE.  The software is provided "as is" without 
 * express or implied warranty of any kind.
 *
 * These notices must be retained in any copies of any part of this 
 * software. 
 */

/*
 * Copyright (c) 1997, 1998 The Regents of the University of California.
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the Network Research
 *      Group at Lawrence Berkeley National Laboratory.
 * 4. Neither the name of the University nor of the Laboratory may be used
 *    to endorse or promote products derived from this software without
 *    specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Full-TCP : A two-way TCP very similar to the 4.4BSD version of Reno TCP.
 * This version also includes variants Tahoe, NewReno, and SACK.
 *
 * This code below has received a fairly major restructuring (Aug. 2001).
 * The ReassemblyQueue structure is now removed to a separate module and
 * entirely re-written.
 * Also, the SACK functionality has been re-written (almost) entirely.
 * -KF [kfall@intel.com]
 *
 * This code below was motivated in part by code contributed by
 * Kathie Nichols (nichols@baynetworks.com).  The code below is based primarily
 * on the 4.4BSD TCP implementation. -KF [kfall@ee.lbl.gov]
 *
 * Kathie Nichols and Van Jacobson have contributed significant bug fixes,
 * especially with respect to the the handling of sequence numbers during
 * connection establishment/clearin.  Additional fixes have followed
 * theirs.
 *
 * Fixes for gensack() and ReassemblyQueue::add() contributed by Richard 
 * Mortier <Richard.Mortier@cl.cam.ac.uk>
 *
 * Some warnings and comments:
 *      this version of TCP will not work correctly if the sequence number
 *      goes above 2147483648 due to sequence number wrap
 *
 *      this version of TCP by default sends data at the beginning of a
 *      connection in the "typical" way... That is,
 *              A   ------> SYN ------> B
 *              A   <----- SYN+ACK ---- B
 *              A   ------> ACK ------> B
 *              A   ------> data -----> B
 *
 *      there is no dynamic receiver's advertised window.   The advertised
 *      window is simulated by simply telling the sender a bound on the window
 *      size (wnd_).
 *
 *      in real TCP, a user process performing a read (via PRU_RCVD)
 *              calls tcp_output each time to (possibly) send a window
 *              update.  Here we don't have a user process, so we simulate
 *              a user process always ready to consume all the receive buffer
 *
 * Notes:
 *      wnd_, wnd_init_, cwnd_, ssthresh_ are in segment units
 *      sequence and ack numbers are in byte units
 *
 * Futures:
 *      there are different existing TCPs with respect to how
 *      ack's are handled on connection startup.  Some delay
 *      the ack for the first segment, which can cause connections
 *      to take longer to start up than if we be sure to ack it quickly.
 *
 *      some TCPs arrange for immediate ACK generation if the incoming segment
 *      contains the PUSH bit
 *
 *
 */

#ifndef lint
static const char rcsid[] =
    "@(#) $Header: /nfs/jade/vint/CVSROOT/ns-2/tcp/tcp-full.cc,v 1.113 2002/07/24 04:34:18 tomh Exp $ (LBL)";
#endif

#include "ip.h"
#include "tcp-full.h"
#include "flags.h"
#include "random.h"
#include "template.h"

#ifndef TRUE
#define TRUE    1
#endif

#ifndef FALSE
#define FALSE   0
#endif

/*
 * Tcl Linkage for the following:
 *      Agent/TCP/FullTcp, Agent/TCP/FullTcp/Tahoe,
 *      Agent/TCP/FullTcp/Newreno, Agent/TCP/FullTcp/Sack
 *
 * See tcl/lib/ns-default.tcl for init methods for
 *      Tahoe, Newreno, and Sack
 */

static class FullTcpClass : public TclClass { 
public:
        FullTcpClass() : TclClass("Agent/TCP/FullTcp") {}
        TclObject* create(int, const char*const*) { 
                return (new FullTcpAgent());
        }
} class_full;

static class TahoeFullTcpClass : public TclClass { 
public:
        TahoeFullTcpClass() : TclClass("Agent/TCP/FullTcp/Tahoe") {}
        TclObject* create(int, const char*const*) { 
                // ns-default sets reno_fastrecov_ to false
                return (new TahoeFullTcpAgent());
        }
} class_tahoe_full;

static class NewRenoFullTcpClass : public TclClass { 
public:
        NewRenoFullTcpClass() : TclClass("Agent/TCP/FullTcp/Newreno") {}
        TclObject* create(int, const char*const*) { 
                // ns-default sets open_cwnd_on_pack_ to false
                return (new NewRenoFullTcpAgent());
        }
} class_newreno_full;

static class SackFullTcpClass : public TclClass { 
public:
        SackFullTcpClass() : TclClass("Agent/TCP/FullTcp/Sack") {}
        TclObject* create(int, const char*const*) { 
                // ns-default sets reno_fastrecov_ to false
                // ns-default sets open_cwnd_on_pack_ to false
                return (new SackFullTcpAgent());
        }
} class_sack_full;

/*
 * Delayed-binding variable linkage
 */

void
FullTcpAgent::delay_bind_init_all()
{
        delay_bind_init_one("segsperack_");
        delay_bind_init_one("segsize_");
        delay_bind_init_one("tcprexmtthresh_");
        delay_bind_init_one("iss_");
        delay_bind_init_one("nodelay_");
        delay_bind_init_one("data_on_syn_");
        delay_bind_init_one("dupseg_fix_");
        delay_bind_init_one("dupack_reset_");
        delay_bind_init_one("close_on_empty_");
        delay_bind_init_one("signal_on_empty_");
        delay_bind_init_one("interval_");
        delay_bind_init_one("ts_option_size_");
        delay_bind_init_one("reno_fastrecov_");
        delay_bind_init_one("pipectrl_");
        delay_bind_init_one("open_cwnd_on_pack_");
        delay_bind_init_one("halfclose_");
        delay_bind_init_one("nopredict_");
        delay_bind_init_one("spa_thresh_");

        TcpAgent::delay_bind_init_all();
       
        reset();
}

int
FullTcpAgent::delay_bind_dispatch(const char *varName, const char *localName, TclObject *tracer)
{
        if (delay_bind(varName, localName, "segsperack_", &segs_per_ack_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "segsize_", &maxseg_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "tcprexmtthresh_", &tcprexmtthresh_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "iss_", &iss_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "spa_thresh_", &spa_thresh_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "nodelay_", &nodelay_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "data_on_syn_", &data_on_syn_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "dupseg_fix_", &dupseg_fix_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "dupack_reset_", &dupack_reset_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "close_on_empty_", &close_on_empty_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "signal_on_empty_", &signal_on_empty_, tracer)) return TCL_OK;
        if (delay_bind_time(varName, localName, "interval_", &delack_interval_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "ts_option_size_", &ts_option_size_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "reno_fastrecov_", &reno_fastrecov_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "pipectrl_", &pipectrl_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "open_cwnd_on_pack_", &open_cwnd_on_pack_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "halfclose_", &halfclose_, tracer)) return TCL_OK;
        if (delay_bind_bool(varName, localName, "nopredict_", &nopredict_, tracer)) return TCL_OK;

        return TcpAgent::delay_bind_dispatch(varName, localName, tracer);
}

void
SackFullTcpAgent::delay_bind_init_all()
{
        delay_bind_init_one("clear_on_timeout_");
        delay_bind_init_one("sack_rtx_cthresh_");
        delay_bind_init_one("sack_rtx_bthresh_");
        delay_bind_init_one("sack_block_size_");
        delay_bind_init_one("sack_option_size_");
        delay_bind_init_one("max_sack_blocks_");
        delay_bind_init_one("sack_rtx_threshmode_");
        FullTcpAgent::delay_bind_init_all();
}

int
SackFullTcpAgent::delay_bind_dispatch(const char *varName, const char *localName, TclObject *tracer)
{
        if (delay_bind_bool(varName, localName, "clear_on_timeout_", &clear_on_timeout_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "sack_rtx_cthresh_", &sack_rtx_cthresh_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "sack_rtx_bthresh_", &sack_rtx_bthresh_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "sack_rtx_threshmode_", &sack_rtx_threshmode_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "sack_block_size_", &sack_block_size_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "sack_option_size_", &sack_option_size_, tracer)) return TCL_OK;
        if (delay_bind(varName, localName, "max_sack_blocks_", &max_sack_blocks_, tracer)) return TCL_OK;
        return FullTcpAgent::delay_bind_dispatch(varName, localName, tracer);
}

int
FullTcpAgent::command(int argc, const char*const* argv)
{
        // would like to have some "connect" primitive
        // here, but the problem is that we get called before
        // the simulation is running and we want to send a SYN.
        // Because no routing exists yet, this fails.
        // Instead, see code in advance().
        //
        // listen can happen any time because it just changes state_
        //
        // close is designed to happen at some point after the
        // simulation is running (using an ns 'at' command)

        if (argc == 2) {
                if (strcmp(argv[1], "listen") == 0) {
                        // just a state transition
                        listen();
                        return (TCL_OK);
                }
                if (strcmp(argv[1], "close") == 0) {
                        usrclosed();
                        return (TCL_OK);
                }
        }
        if (argc == 3) {
                if (strcmp(argv[1], "advance") == 0) {
                        advanceby(atoi(argv[2]));
                        return (TCL_OK);
                }
                if (strcmp(argv[1], "advanceby") == 0) {
                        advanceby(atoi(argv[2]));
                        return (TCL_OK);
                }
                if (strcmp(argv[1], "advance-bytes") == 0) {
                        advance_bytes(atoi(argv[2]));
                        return (TCL_OK);
                }
        }
        if (argc == 4) {
                if (strcmp(argv[1], "sendmsg") == 0) {
                        sendmsg(atoi(argv[2]), argv[3]);
                        return (TCL_OK);
                }
        }
        return (TcpAgent::command(argc, argv));
}

/*
 * "User Interface" Functions for Full TCP
 *      advanceby(number of packets)
 *      advance_bytes(number of bytes)
 *      sendmsg(int bytes, char* buf)
 *      listen
 *      close
 */

/*
 * the 'advance' interface to the regular tcp is in packet
 * units.  Here we scale this to bytes for full tcp.
 *
 * 'advance' is normally called by an "application" (i.e. data source)
 * to signal that there is something to send
 *
 * 'curseq_' is the sequence number of the last byte provided
 * by the application.  In the case where no data has been supplied
 * by the application, curseq_ is the iss_.
 */
void
FullTcpAgent::advanceby(int np)
{
        // XXX hack:
        //      because np is in packets and a data source
        //      may pass a *huge* number as a way to tell us
        //      to go forever, just look for the huge number
        //      and if it's there, pre-divide it
        if (np >= 0x10000000)
                np /= maxseg_;

        advance_bytes(np * maxseg_);
        return;
}

/*
 * the byte-oriented interface: advance_bytes(int nbytes)
 */

void
FullTcpAgent::advance_bytes(int nb)
{

        //
        // state-specific operations:
        //      if CLOSED or LISTEN, reset and try a new active open/connect
        //      if ESTABLISHED, queue and try to send more
        //      if SYN_SENT or SYN_RCVD, just queue
        //      if above ESTABLISHED, we are closing, so don't allow
        //

        switch (state_) {

        case TCPS_CLOSED:
        case TCPS_LISTEN:
                reset();
                curseq_ = iss_ + nb;
                connect();              // initiate new connection
                break;

        case TCPS_ESTABLISHED:
        case TCPS_SYN_SENT:
        case TCPS_SYN_RECEIVED:
                if (curseq_ < iss_) 
                        curseq_ = iss_; 
                curseq_ += nb;
                break;

        default:
            fprintf(stderr,
            "%f: FullTcpAgent::advance(%s): cannot advance while in state %s\n",
                 now(), name(), statestr(state_));

        }

        if (state_ == TCPS_ESTABLISHED)
                send_much(0, REASON_NORMAL, maxburst_);

        return;
}

/*
 * If MSG_EOF is set, by setting close_on_empty_ to TRUE, we ensure that
 * a FIN will be sent when the send buffer emptys.
 * If DAT_EOF is set, the callback function done_data is called
 * when the send buffer empty
 * 
 * When (in the future?) FullTcpAgent implements T/TCP, avoidance of 3-way 
 * handshake can be handled in this function.
 */
void
FullTcpAgent::sendmsg(int nbytes, const char *flags)
{
        if (flags && strcmp(flags, "MSG_EOF") == 0) 
                close_on_empty_ = TRUE; 
        if (flags && strcmp(flags, "DAT_EOF") == 0) 
                signal_on_empty_ = TRUE;        

        if (nbytes == -1) {
                infinite_send_ = TRUE;
                advance_bytes(0);
        } else
                advance_bytes(nbytes);
}

/*
 * do an active open
 * (in real TCP, see tcp_usrreq, case PRU_CONNECT)
 */
void
FullTcpAgent::connect()
{
        newstate(TCPS_SYN_SENT);        // sending a SYN now
        sent(iss_, foutput(iss_, REASON_NORMAL));
        return;
}

/*
 * be a passive opener
 * (in real TCP, see tcp_usrreq, case PRU_LISTEN)
 * (for simulation, make this peer's ptype ACKs)
 */
void
FullTcpAgent::listen()
{
        newstate(TCPS_LISTEN);
        type_ = PT_ACK; // instead of PT_TCP
}


/*
* This function is invoked when the sender buffer is empty. It in turn
* invokes the Tcl done_data procedure that was registered with TCP.
*/
 
void
FullTcpAgent::bufferempty()
{
        signal_on_empty_=FALSE;
        Tcl::instance().evalf("%s done_data", this->name());
}


/*
 * called when user/application performs 'close'
 */

void
FullTcpAgent::usrclosed()
{
        curseq_ = maxseq_ - 1;  // now, no more data
        infinite_send_ = FALSE; // stop infinite send

        switch (state_) {
        case TCPS_CLOSED:
        case TCPS_LISTEN:
                cancel_timers();
                newstate(TCPS_CLOSED);
                finish();
                break;
        case TCPS_SYN_SENT:
                newstate(TCPS_CLOSED);
                /* fall through */
        case TCPS_LAST_ACK:
                flags_ |= TF_NEEDFIN;
                send_much(1, REASON_NORMAL, maxburst_);
                break;
        case TCPS_SYN_RECEIVED:
        case TCPS_ESTABLISHED:
                newstate(TCPS_FIN_WAIT_1);
                flags_ |= TF_NEEDFIN;
                send_much(1, REASON_NORMAL, maxburst_);
                break;
        case TCPS_CLOSE_WAIT:
                newstate(TCPS_LAST_ACK);
                flags_ |= TF_NEEDFIN;
                send_much(1, REASON_NORMAL, maxburst_);
                break;
        case TCPS_FIN_WAIT_1:
        case TCPS_FIN_WAIT_2:
        case TCPS_CLOSING:
                /* usr asked for a close more than once [?] */
                fprintf(stderr,
                  "%f FullTcpAgent(%s): app close in bad state %s\n",
                  now(), name(), statestr(state_));
                break;
        default:
                fprintf(stderr,
                  "%f FullTcpAgent(%s): app close in unknown state %s\n",
                  now(), name(), statestr(state_));
        }

        return;
}

/*
 * Utility type functions
 */

void
FullTcpAgent::cancel_timers()
{

        // cancel: rtx, burstsend, delsnd
        TcpAgent::cancel_timers();      
        // cancel: delack
        delack_timer_.force_cancel();
}

void
FullTcpAgent::newstate(int state)
{
//printf("%f(%s): state changed from %s to %s\n",
//now(), name(), statestr(state_), statestr(state));

        state_ = state;
}

void
FullTcpAgent::prpkt(Packet *pkt)
{
        hdr_tcp *tcph = hdr_tcp::access(pkt);   // TCP header
        hdr_cmn *th = hdr_cmn::access(pkt);     // common header (size, etc)
        //hdr_flags *fh = hdr_flags::access(pkt);       // flags (CWR, CE, bits)
        hdr_ip* iph = hdr_ip::access(pkt);
        int datalen = th->size() - tcph->hlen(); // # payload bytes

        fprintf(stdout, " [%d:%d.%d>%d.%d] (hlen:%d, dlen:%d, seq:%d, ack:%d, flags:0x%x (%s), salen:%d, reason:0x%x)\n",
                th->uid(),
                iph->saddr(), iph->sport(),
                iph->daddr(), iph->dport(),
                tcph->hlen(),
                datalen,
                tcph->seqno(),
                tcph->ackno(),
                tcph->flags(), flagstr(tcph->flags()),
                tcph->sa_length(),
                tcph->reason());
}

char *
FullTcpAgent::flagstr(int hflags)
{
        // update this if tcp header flags change
        static char *flagstrs[28] = {
                "<null>", "<FIN>", "<SYN>", "<SYN,FIN>",        // 0-3
                "<?>", "<?,FIN>", "<?,SYN>", "<?,SYN,FIN>",     // 4-7
                "<PSH>", "<PSH,FIN>", "<PSH,SYN>", "<PSH,SYN,FIN>", // 0x08-0x0b
                /* do not use <??, in next line because that's an ANSI trigraph */
                "<?>", "<?,FIN>", "<?,SYN>", "<?,SYN,FIN>",         // 0x0c-0x0f
                "<ACK>", "<ACK,FIN>", "<ACK,SYN>", "<ACK,SYN,FIN>", // 0x10-0x13
                "<ACK>", "<ACK,FIN>", "<ACK,SYN>", "<ACK,SYN,FIN>", // 0x14-0x17
                "<PSH,ACK>", "<PSH,ACK,FIN>", "<PSH,ACK,SYN>", "<PSH,ACK,SYN,FIN>", // 0x18-0x1b
        };
        if (hflags < 0 || (hflags > 28))
                return ("<invalid>");
        return (flagstrs[hflags]);
}

char *
FullTcpAgent::statestr(int state)
{
        static char *statestrs[TCP_NSTATES] = {
                "CLOSED", "LISTEN", "SYN_SENT", "SYN_RCVD",
                "ESTABLISHED", "CLOSE_WAIT", "FIN_WAIT_1", "CLOSING",
                "LAST_ACK", "FIN_WAIT_2"
        };
        if (state < 0 || (state >= TCP_NSTATES))
                return ("INVALID");
        return (statestrs[state]);
}

void
DelAckTimer::expire(Event *) {
        a_->timeout(TCP_TIMER_DELACK);
}

/*
 * reset to starting point, don't set state_ here,
 * because our starting point might be LISTEN rather
 * than CLOSED if we're a passive opener
 */
void
FullTcpAgent::reset()
{
        cancel_timers();        // cancel timers first
        TcpAgent::reset();      // resets most variables
        rq_.clear();            // clear reassembly queue
        rtt_init();             // zero rtt, srtt, backoff

        last_ack_sent_ = -1;
        rcv_nxt_ = -1;
        pipe_ = 0;
        rtxbytes_ = 0;
        flags_ = 0;
        t_seqno_ = iss_;
        maxseq_ = -1;
        irs_ = -1;
        last_send_time_ = -1.0;
        if (ts_option_)
                recent_ = recent_age_ = 0.0;
        else
                recent_ = recent_age_ = -1.0;

        fastrecov_ = FALSE;
}

/*
 * This function is invoked when the connection is done. It in turn
 * invokes the Tcl finish procedure that was registered with TCP.
 * This function mimics tcp_close()
 */

void
FullTcpAgent::finish()
{
        Tcl::instance().evalf("%s done", this->name());
}
/*
 * headersize:
 *      how big is an IP+TCP header in bytes; include options such as ts
 * this function should be virtual so others (e.g. SACK) can override
 */
int
FullTcpAgent::headersize()
{
        int total = tcpip_base_hdr_size_;
        if (total < 1) {
                fprintf(stderr,
                    "%f: FullTcpAgent(%s): warning: tcpip hdr size is only %d bytes\n",
                        now(), name(), tcpip_base_hdr_size_);
        }

        if (ts_option_)
                total += ts_option_size_;

        return (total);
}

/*
 * flags that are completely dependent on the tcp state
 * these are used for the next outgoing packet in foutput()
 * (in real TCP, see tcp_fsm.h, the "tcp_outflags" array)
 */
int
FullTcpAgent::outflags()
{
        // in real TCP an RST is added in the CLOSED state
        static int tcp_outflags[TCP_NSTATES] = {
                TH_ACK,                 /* 0, CLOSED */  
                0,                      /* 1, LISTEN */ 
                TH_SYN,                 /* 2, SYN_SENT */
                TH_SYN|TH_ACK,          /* 3, SYN_RECEIVED */
                TH_ACK,                 /* 4, ESTABLISHED */
                TH_ACK,                 /* 5, CLOSE_WAIT */
                TH_FIN|TH_ACK,          /* 6, FIN_WAIT_1 */
                TH_FIN|TH_ACK,          /* 7, CLOSING */
                TH_FIN|TH_ACK,          /* 8, LAST_ACK */
                TH_ACK,                 /* 9, FIN_WAIT_2 */
                /* 10, TIME_WAIT --- not used in simulator */
        };

        if (state_ < 0 || (state_ >= TCP_NSTATES)) {
                fprintf(stderr, "%f FullTcpAgent(%s): invalid state %d\n",
                        now(), name(), state_);
                return (0x0);
        }

        return (tcp_outflags[state_]);
}

/*
 * reaass() -- extract the appropriate fields from the packet
 *      and pass this info the ReassemblyQueue add routine
 *
 * returns the TCP header flags representing the "or" of
 *      the flags contained in the adjacent sequence # blocks
 */

int
FullTcpAgent::reass(Packet* pkt)
{  
        hdr_tcp *tcph =  hdr_tcp::access(pkt);
        hdr_cmn *th = hdr_cmn::access(pkt);
   
        int start = tcph->seqno();
        int end = start + th->size() - tcph->hlen();
        int tiflags = tcph->flags();
        int fillshole = (start == rcv_nxt_);
        int flags;
   
        // end contains the seq of the last byte of
        // in the packet plus one

        if (start == end && (tiflags & TH_FIN) == 0) {
                fprintf(stderr, "%f: FullTcpAgent(%s)::reass() -- bad condition - adding non-FIN zero-len seg\n",
                        now(), name());
                abort();
        }

        flags = rq_.add(start, end, tiflags, 0);

        //present:
        //
        // If we've never received a SYN (unlikely)
        // or this is an out of order addition, no reason to coalesce
        //

        if (TCPS_HAVERCVDSYN(state_) == 0 || !fillshole) {
                return (0x00);
        }
        //
        // If we get some data in SYN_RECVD, no need to present to user yet
        //
        if (state_ == TCPS_SYN_RECEIVED && (end > start))
                return (0x00);

        // clear out data that has been passed, up to rcv_nxt_,
        // collects flags

        flags |= rq_.cleartonxt();

        return (flags);
}

/*
 * utility function to set rcv_next_ during inital exchange of seq #s
 */

int
FullTcpAgent::rcvseqinit(int seq, int dlen)
{
        return (seq + dlen + 1);
}

/*
 * build a header with the timestamp option if asked
 */
int
FullTcpAgent::build_options(hdr_tcp* tcph)
{
        int total = 0;
        if (ts_option_) {
                tcph->ts() = now();
                tcph->ts_echo() = recent_;
                total += ts_option_size_;
        } else {
                tcph->ts() = tcph->ts_echo() = -1.0;
        }
        return (total);
}

/*
 * pack() -- is the ACK a partial ACK? (not past recover_)
 */

int
FullTcpAgent::pack(Packet *pkt)
{
        hdr_tcp *tcph = hdr_tcp::access(pkt);
        return (tcph->ackno() >= highest_ack_ &&
                tcph->ackno() < recover_);
}

/*
 * baseline reno TCP exists fast recovery on a partial ACK
 */

void
FullTcpAgent::pack_action(Packet*)
{
        if (reno_fastrecov_ && fastrecov_ && cwnd_ > double(ssthresh_)) {
                cwnd_ = double(ssthresh_); // retract window if inflated
        }
        fastrecov_ = FALSE;
//printf("%f: EXITED FAST RECOVERY\n", now());
        dupacks_ = 0;
}

/*
 * ack_action -- same as partial ACK action for base Reno TCP
 */

void
FullTcpAgent::ack_action(Packet* p)
{
        FullTcpAgent::pack_action(p);
}


/*
 * sendpacket: 
 *      allocate a packet, fill in header fields, and send
 *      also keeps stats on # of data pkts, acks, re-xmits, etc
 *
 * fill in packet fields.  Agent::allocpkt() fills
 * in most of the network layer fields for us.
 * So fill in tcp hdr and adjust the packet size.
 *
 * Also, set the size of the tcp header.
 */
void
FullTcpAgent::sendpacket(int seqno, int ackno, int pflags, int datalen, int reason)
{
        Packet* p = allocpkt();
        hdr_tcp *tcph = hdr_tcp::access(p);
        hdr_flags *fh = hdr_flags::access(p);

        /* build basic header w/options */

        tcph->seqno() = seqno;
        tcph->ackno() = ackno;
        tcph->flags() = pflags;
        tcph->reason() |= reason; // make tcph->reason look like ns1 pkt->flags?
        tcph->sa_length() = 0;    // may be increased by build_options()
        tcph->hlen() = tcpip_base_hdr_size_;
        tcph->hlen() += build_options(tcph);

        /*
         * Explicit Congestion Notification (ECN) related:
         * Bits in header:
         *      ECT (EC Capable Transport),
         *      ECNECHO (ECHO of ECN Notification generated at router),
         *      CWR (Congestion Window Reduced from RFC 2481)
         * States in TCP:
         *      ecn_: I am supposed to do ECN if my peer does
         *      ect_: I am doing ECN (ecn_ should be T and peer does ECN)
         */

        // set ect on data packets (not syn or ack packets)
        if ( datalen > 0 && ecn_ ){
                fh->ect() = ect_;       // on after mutual agreement on ECT
        }

        // fill in CWR and ECE bits which don't actually sit in
        // the tcp_flags but in hdr_flags
        if ( pflags & TH_ECE) {
                fh->ecnecho() = 1;
        } else {
                fh->ecnecho() = 0;
        }
        if ( pflags & TH_CWR ) {
                fh->cong_action() = 1;
        }

        //
        // although CWR bit is ordinarily associated with ECN,
        // it utility within the simulator for traces.  Thus, set
        // it even if we aren't doing ECN
        //
        if ( datalen > 0 )
                fh->cwr() =  cong_action_;

        /* actual size is data length plus header length */

        hdr_cmn *ch = hdr_cmn::access(p);
        ch->size() = datalen + tcph->hlen();

        if (datalen <= 0)
                ++nackpack_;
        else {
                ++ndatapack_;
                ndatabytes_ += datalen;
                last_send_time_ = now();        // time of last data
        }
        if (reason == REASON_TIMEOUT || reason == REASON_DUPACK || reason == REASON_SACK) {
                ++nrexmitpack_;
                nrexmitbytes_ += datalen;
        }

        last_ack_sent_ = ackno;

//if (state_ != TCPS_ESTABLISHED) {
//printf("%f(%s)[state:%s]: sending pkt ", now(), name(), statestr(state_));
//prpkt(p);
//}

        send(p, 0);

        return;
}

//
// reset_rtx_timer: called during a retransmission timeout
// to perform exponential backoff.  Also, note that because
// we have performed a retransmission, our rtt timer is now
// invalidated (indicate this by setting rtt_active_ false)
//
void
FullTcpAgent::reset_rtx_timer(int /* mild */)
{
        // cancel old timer, set a new one
        /* if there is no outstanding data, don't back off rtx timer *
         * (Fix from T. Kelly.) */
        if (!(highest_ack_ == maxseq_ && restart_bugfix_)) {
                rtt_backoff();          // double current timeout
        }
        set_rtx_timer();        // set new timer
        rtt_active_ = FALSE;    // no timing during this window
}

/*
 * see if we should send a segment, and if so, send it
 *      (may be ACK or data)
 * return the number of data bytes sent (count a SYN or FIN as 1 each)
 *
 * simulator var, desc (name in real TCP)
 * --------------------------------------
 * maxseq_, largest seq# we've sent plus one (snd_max)
 * flags_, flags regarding our internal state (t_state)
 * pflags, a local used to build up the tcp header flags (flags)
 * curseq_, is the highest sequence number given to us by "application"
 * highest_ack_, the highest ACK we've seen for our data (snd_una-1)
 * seqno, the next seq# we're going to send (snd_nxt)
 */
int
FullTcpAgent::foutput(int seqno, int reason)
{
        // if maxseg_ not set, set it appropriately
        // Q: how can this happen?

        if (maxseg_ == 0) 
                maxseg_ = size_ - headersize();
        else
                size_ =  maxseg_ + headersize();

        int is_retransmit = (seqno < maxseq_);
        int quiet = (highest_ack_ == maxseq_);
        int pflags = outflags();
        int syn = (seqno == iss_);
        int emptying_buffer = FALSE;
        int buffered_bytes = (infinite_send_) ? TCP_MAXSEQ :
                                curseq_ - highest_ack_ + 1;

        int win = window() * maxseg_;   // window (in bytes)
        int off = seqno - highest_ack_; // offset of seg in window
        int datalen;
        //int amtsent = 0;

        // be careful if we have not received any ACK yet
        if (highest_ack_ < 0) {
                if (!infinite_send_)
                        buffered_bytes = curseq_ - iss_;;
                off = seqno - iss_;
        }

        if (syn && !data_on_syn_)
                datalen = 0;
        else if (pipectrl_)
                datalen = buffered_bytes - off;
        else
                datalen = min(buffered_bytes, win) - off;

        if ((signal_on_empty_) && (!buffered_bytes) && (!syn))
                        bufferempty();

        //
        // in real TCP datalen (len) could be < 0 if there was window
        // shrinkage, or if a FIN has been sent and neither ACKd nor
        // retransmitted.  Only this 2nd case concerns us here...
        //
        if (datalen < 0) {
                datalen = 0;
        } else if (datalen > maxseg_) {
                datalen = maxseg_;
        }


        //
        // this is an option that causes us to slow-start if we've
        // been idle for a "long" time, where long means a rto or longer
        // the slow-start is a sort that does not set ssthresh
        //

        if (slow_start_restart_ && quiet && datalen > 0) {
                if (idle_restart()) {
                        slowdown(CLOSE_CWND_INIT);
                }
        }

        //
        // see if sending this packet will empty the send buffer
        // a dataless SYN packet counts also
        //

        if (!infinite_send_ && ((seqno + datalen) > curseq_ || 
            (syn && datalen == 0))) {
                emptying_buffer = TRUE;
                //
                // if not a retransmission, notify application that 
                // everything has been sent out at least once.
                //
                if (!syn) {
                        idle();
                        if (close_on_empty_ && quiet) {
                                flags_ |= TF_NEEDCLOSE;
                        }
                }
                pflags |= TH_PUSH;
                //
                // if close_on_empty set, we are finished
                // with this connection; close it
                //
        } else  {
                /* not emptying buffer, so can't be FIN */
                pflags &= ~TH_FIN;
        }
        if (infinite_send_ && (syn && datalen == 0))
                pflags |= TH_PUSH;  // set PUSH for dataless SYN

        /* sender SWS avoidance (Nagle) */

        if (datalen > 0) {
                // if full-sized segment, ok
                if (datalen == maxseg_)
                        goto send;
                // if Nagle disabled and buffer clearing, ok
                if ((quiet || nodelay_)  && emptying_buffer)
                        goto send;
                // if a retransmission
                if (is_retransmit)
                        goto send;
                // if big "enough", ok...
                //      (this is not a likely case, and would
                //      only happen for tiny windows)
                if (datalen >= ((wnd_ * maxseg_) / 2.0))
                        goto send;
        }

        if (need_send())
                goto send;

        /*
         * send now if a control packet or we owe peer an ACK
         * TF_ACKNOW can be set during connection establishment and
         * to generate acks for out-of-order data
         */

        if ((flags_ & (TF_ACKNOW|TF_NEEDCLOSE)) ||
            (pflags & (TH_SYN|TH_FIN))) {
                goto send;
        }

        /*      
         * No reason to send a segment, just return.
         */      
        return 0;

send:

        // is a syn or fin?

        syn = (pflags & TH_SYN) ? 1 : 0;
        int fin = (pflags & TH_FIN) ? 1 : 0;

        /* setup ECN syn and ECN SYN+ACK packet headers */
        if (ecn_ && syn && !(pflags & TH_ACK)){
                pflags |= TH_ECE;
                pflags |= TH_CWR;
        }
        if (ecn_ && syn && (pflags & TH_ACK)){
                pflags |= TH_ECE;
                pflags &= ~TH_CWR;
        }
  
        /* set CWR if necessary */
        if (ecn_ && ect_ && cong_action_) pflags |= TH_CWR;
  
        /* set ECE if necessary */
        if (ecn_ && ect_ && recent_ce_ ) pflags |= TH_ECE;

        /* 
         * Tack on the FIN flag to the data segment if close_on_empty_
         * was previously set-- avoids sending a separate FIN
         */ 
        if (flags_ & TF_NEEDCLOSE) {
                flags_ &= ~TF_NEEDCLOSE;
                if (state_ <= TCPS_ESTABLISHED && state_ != TCPS_CLOSED)
                {
                    pflags |=TH_FIN;
                    fin = 1;  /* FIN consumes sequence number */
                    newstate(TCPS_FIN_WAIT_1);
                }
        }
        sendpacket(seqno, rcv_nxt_, pflags, datalen, reason);

        /*      
         * Data sent (as far as we can tell).
         * Any pending ACK has now been sent.
         */      
        flags_ &= ~(TF_ACKNOW|TF_DELACK);

        /*
         * if we have reacted to congestion recently, the
         * slowdown() procedure will have set cong_action_ and
         * sendpacket will have copied that to the outgoing pkt
         * CWR field. If that packet contains data, then
         * it will be reliably delivered, so we are free to turn off the
         * cong_action_ state now  If only a pure ACK, we keep the state
         * around until we actually send a segment
         */

        int reliable = datalen + syn + fin; // seq #'s reliably sent
        if (cong_action_ && reliable > 0)
                cong_action_ = FALSE;

        // highest: greatest sequence number sent + 1
        //      and adjusted for SYNs and FINs which use up one number

        int highest = seqno + reliable;
        if (highest > maxseq_) {
                maxseq_ = highest;
                //
                // if we are using conventional RTT estimation,
                // establish timing on this segment
                //
                if (!ts_option_ && rtt_active_ == FALSE) {
                        rtt_active_ = TRUE;     // set timer
                        rtt_seq_ = seqno;       // timed seq #
                        rtt_ts_ = now();        // when set
                }
        }

        /*
         * Set retransmit timer if not currently set,
         * and not doing an ack or a keep-alive probe.
         * Initial value for retransmit timer is smoothed
         * round-trip time + 2 * round-trip time variance.
         * Future values are rtt + 4 * rttvar.
         */
        if (rtx_timer_.status() != TIMER_PENDING && reliable) {
                set_rtx_timer();  // no timer pending, schedule one
        }

        return (reliable);
}

/*
 *
 * send_much: send as much data as we are allowed to.  This is
 * controlled by the "pipectrl_" variable.  If pipectrl_ is set
 * to FALSE, then we are working as a normal window-based TCP and
 * we are allowed to send whatever the window allows.
 * If pipectrl_ is set to TRUE, then we are allowed to send whatever
 * pipe_ allows us to send.  One tricky part is to make sure we
 * do not overshoot the receiver's advertised window if we are
 * in (pipectrl_ == TRUE) mode.
 */
  
void
FullTcpAgent::send_much(int force, int reason, int maxburst)
{
        int npackets = 0;       // sent so far

//if ((int(t_seqno_)) > 1)
//printf("%f: send_much(f:%d, win:%d, pipectrl:%d, pipe:%d, t_seqno:%d, topwin:%d, maxseq_:%d\n",
//now(), force, win, pipectrl_, pipe_, int(t_seqno_), topwin, int(maxseq_));

        if (!force && (delsnd_timer_.status() == TIMER_PENDING))
                return;

        while (1) {

                /*
                 * note that if output decides to not actually send
                 * (e.g. because of Nagle), then if we don't break out
                 * of this loop, we can loop forever at the same
                 * simulated time instant
                 */
                int amt;
                int seq = nxt_tseq();
                if (!force && !send_allowed(seq))
                        break;
                // Q: does this need to be here too?
                if (!force && overhead_ != 0 &&
                    (delsnd_timer_.status() != TIMER_PENDING)) {
                        delsnd_timer_.resched(Random::uniform(overhead_));
                        return;
                }
                if ((amt = foutput(seq, reason)) <= 0)
                        break;
                if ((outflags() & TH_FIN))
                        --amt;  // don't count FINs
                sent(seq, amt);
                force = 0;

                if ((outflags() & (TH_SYN|TH_FIN)) ||
                    (maxburst && ++npackets >= maxburst))
                        break;
        }
        return;
}

/*
 * base TCP: we are allowed to send a sequence number if it
 * is in the window
 */
int
FullTcpAgent::send_allowed(int seq)
{
        int win = window() * maxseg_;
        int topwin = curseq_; // 1 seq number past the last byte we can send

        if ((topwin > highest_ack_ + win) || infinite_send_)
                topwin = highest_ack_ + win; 

        return (seq < topwin);
}
/*
 * Process an ACK
 *      this version of the routine doesn't necessarily
 *      require the ack to be one which advances the ack number
 *
 * if this ACKs a rtt estimate
 *      indicate we are not timing
 *      reset the exponential timer backoff (gamma)
 * update rtt estimate
 * cancel retrans timer if everything is sent and ACK'd, else set it
 * advance the ack number if appropriate
 * update segment to send next if appropriate
 */
void
FullTcpAgent::newack(Packet* pkt)
{
        hdr_tcp *tcph = hdr_tcp::access(pkt);

        register int ackno = tcph->ackno();
        int progress = (ackno > highest_ack_);

        if (ackno == maxseq_) {
                cancel_rtx_timer();     // all data ACKd
        } else if (progress) {
                set_rtx_timer();
        }

        // advance the ack number if this is for new data
        if (progress)
                highest_ack_ = ackno;

        // if we have suffered a retransmit timeout, t_seqno_
        // will have been reset to highest_ ack.  If the
        // receiver has cached some data above t_seqno_, the
        // new-ack value could (should) jump forward.  We must
        // update t_seqno_ here, otherwise we would be doing
        // go-back-n.

        if (t_seqno_ < highest_ack_)
                t_seqno_ = highest_ack_; // seq# to send next

        /*
         * Update RTT only if it's OK to do so from info in the flags header.
         * This is needed for protocols in which intermediate agents
         * in the network intersperse acks (e.g., ack-reconstructors) for
         * various reasons (without violating e2e semantics).
         */
        hdr_flags *fh = hdr_flags::access(pkt);

        if (!fh->no_ts_) {
                if (ts_option_) {
                        recent_age_ = now();
                        recent_ = tcph->ts();
                        rtt_update(now() - tcph->ts_echo());
                } else if (rtt_active_ && ackno > rtt_seq_) {
                        // got an RTT sample, record it
                        // "t_backoff_ = 1;" deleted by T. Kelly.
                        rtt_active_ = FALSE;
                        rtt_update(now() - rtt_ts_);
                }

                if (!ect_ || !ecn_backoff_ ||
                    !hdr_flags::access(pkt)->ecnecho()) {
                        /*
                         * Don't end backoff if still in ECN-Echo with
                         * a congestion window of 1 packet.
                         * Fix from T. Kelly.
                         */
                        t_backoff_ = 1;
                        ecn_backoff_ = 0;
                }
        }
        return;
}

/*
 * this is the simulated form of the header prediction
 * predicate.  While not really necessary for a simulation, it
 * follows the code base more closely and can sometimes help to reveal
 * odd behavior caused by the implementation structure..
 *
 * Here's the comment from the real TCP:
 *
 * Header prediction: check for the two common cases
 * of a uni-directional data xfer.  If the packet has
 * no control flags, is in-sequence, the window didn't
 * change and we're not retransmitting, it's a
 * candidate.  If the length is zero and the ack moved
 * forward, we're the sender side of the xfer.  Just
 * free the data acked & wake any higher level process
 * that was blocked waiting for space.  If the length
 * is non-zero and the ack didn't move, we're the
 * receiver side.  If we're getting packets in-order
 * (the reassembly queue is empty), add the data to
 * the socket buffer and note that we need a delayed ack.
 * Make sure that the hidden state-flags are also off.
 * Since we check for TCPS_ESTABLISHED above, it can only
 * be TF_NEEDSYN.
 */

int
FullTcpAgent::predict_ok(Packet* pkt)
{
        hdr_tcp *tcph = hdr_tcp::access(pkt);
        hdr_flags *fh = hdr_flags::access(pkt);

        /* not the fastest way to do this, but perhaps clearest */

        int p1 = (state_ == TCPS_ESTABLISHED);          // ready
        int p2 = ((tcph->flags() & (TH_SYN|TH_FIN|TH_ACK)) == TH_ACK); // ACK
        int p3 = ((flags_ & TF_NEEDFIN) == 0);          // don't need fin
        int p4 = (!ts_option_ || fh->no_ts_ || (tcph->ts() >= recent_)); // tsok
        int p5 = (tcph->seqno() == rcv_nxt_);           // in-order data
        int p6 = (t_seqno_ == maxseq_);                 // not re-xmit
        int p7 = (!ecn_ || fh->ecnecho() == 0);         // no ECN
        int p8 = (tcph->sa_length() == 0);              // no SACK info

        return (p1 && p2 && p3 && p4 && p5 && p6 && p7 && p8);
}

/*
 * fast_retransmit using the given seqno
 *      perform fast RTX, set recover_, set last_cwnd_action
 */

int
FullTcpAgent::fast_retransmit(int seq)
{
        // we are now going to fast-retransmit and willtrace that event
        trace_event("FAST_RETX");
        
        recover_ = maxseq_;     // recovery target
        last_cwnd_action_ = CWND_ACTION_DUPACK;
        return(foutput(seq, REASON_DUPACK));    // send one pkt
}

/*
 * real tcp determines if the remote
 * side should receive a window update/ACK from us, and often
 * results in sending an update every 2 segments, thereby
 * giving the familiar 2-packets-per-ack behavior of TCP.
 * Here, we don't advertise any windows, so we just see if
 * there's at least 'segs_per_ack_' pkts not yet acked
 *
 * also, provide for a segs-per-ack "threshold" where
 * we generate 1-ack-per-seg until enough stuff
 * (spa_thresh_ bytes) has been received from the other side
 * This idea came from vj/kmn in BayTcp.  Added 8/21/01.
 */

int
FullTcpAgent::need_send()
{
        if (flags_ & TF_ACKNOW)
                return TRUE;

        int spa = (spa_thresh_ > 0 && ((rcv_nxt_ - irs_)  < spa_thresh_)) ?
                1 : segs_per_ack_;
                
        return ((rcv_nxt_ - last_ack_sent_) >= (spa * maxseg_));
}

/*
 * determine whether enough time has elapsed in order to
 * conclude a "restart" is necessary (e.g. a slow-start)
 *
 * for now, keep track of this similarly to how rtt_update() does
 */

int
FullTcpAgent::idle_restart()
{
        if (last_send_time_ < 0.0) {
                // last_send_time_ isn't set up yet, we shouldn't
                // do the idle_restart
                return (0);
        }

        double tao = now() - last_send_time_;
        if (!ts_option_) {
                double tickoff = fmod(last_send_time_ + boot_time_,
                        tcp_tick_);
                tao = int((tao + tickoff) / tcp_tick_) * tcp_tick_;
        }

        return (tao > t_rtxcur_);  // verify this CHECKME
}

/*
 * tcp-full's version of set_initial_window()... over-rides
 * the one in tcp.cc
 */
void
FullTcpAgent::set_initial_window()
{
        syn_ = TRUE;    // full-tcp always models SYN exchange
        TcpAgent::set_initial_window();
}       

/*
 * main reception path - 
 * called from the agent that handles the data path below in its muxing mode
 * advance() is called when connection is established with size sent from
 * user/application agent
 *
 * This is a fairly complex function.  It operates generally as follows:
 *      do header prediction for simple cases (pure ACKS or data)
 *      if in LISTEN and we get a SYN, begin initializing connection
 *      if in SYN_SENT and we get an ACK, complete connection init
 *      trim any redundant data from received dataful segment
 *      deal with ACKS:
 *              if in SYN_RCVD, complete connection init then go on
 *              see if ACK is old or at the current highest_ack
 *              if at current high, is the threshold reached or not
 *              if so, maybe do fast rtx... otherwise drop or inflate win
 *      deal with incoming data
 *      deal with FIN bit on in arriving packet
 */
void
FullTcpAgent::recv(Packet *pkt, Handler*)
{
        hdr_tcp *tcph = hdr_tcp::access(pkt);   // TCP header
        hdr_cmn *th = hdr_cmn::access(pkt);     // common header (size, etc)
        hdr_flags *fh = hdr_flags::access(pkt); // flags (CWR, CE, bits)

        int needoutput = FALSE;
        int ourfinisacked = FALSE;
        int dupseg = FALSE;                     // recv'd dup data segment
        int todrop = 0;                         // duplicate DATA cnt in seg

        last_state_ = state_;

        int datalen = th->size() - tcph->hlen(); // # payload bytes
        int ackno = tcph->ackno();               // ack # from packet
        int tiflags = tcph->flags() ;            // tcp flags from packet

//if (state_ != TCPS_ESTABLISHED || (tiflags&(TH_SYN|TH_FIN))) {
//fprintf(stdout, "%f(%s)in state %s recv'd this packet: ", now(), name(), statestr(state_));
//prpkt(pkt);
//}

        /*
         * Don't expect to see anything while closed
         */

        if (state_ == TCPS_CLOSED) {
                fprintf(stderr, "%f: FullTcp(%s): recv'd pkt in CLOSED state: ",
                        now(), name());
                prpkt(pkt);
                goto drop;
        }

        /*
         * Process options if not in LISTEN state,
         * else do it below
         */

        if (state_ != TCPS_LISTEN)
                dooptions(pkt);

        /*
         * if we are using delayed-ACK timers and
         * no delayed-ACK timer is set, set one.
         * They are set to fire every 'interval_' secs, starting
         * at time t0 = (0.0 + k * interval_) for some k such
         * that t0 > now
         */

        if (delack_interval_ > 0.0 &&
            (delack_timer_.status() != TIMER_PENDING)) {
                int last = int(now() / delack_interval_);
                delack_timer_.resched(delack_interval_ * (last + 1.0) - now());
        }

        /*
         * sanity check for ECN: shouldn't be seeing a CE bit if
         * ECT wasn't set on the packet first.  If we see this, we
         * probably have a misbehaving router...
         */

        if (fh->ce() && !fh->ect()) {
            fprintf(stderr,
            "%f: FullTcpAgent::recv(%s): warning: CE bit on, but ECT false!\n",
                now(), name());
        }

        /*
         * Try header prediction: in seq data or in seq pure ACK
         *      with no funny business
         */

        if (!nopredict_ && predict_ok(pkt)) {
                /*
                 * If last ACK falls within this segment's sequence numbers,
                 * record the timestamp.
                 * See RFC1323 (now RFC1323 bis)
                 */
                if (ts_option_ && !fh->no_ts_ &&
                    tcph->seqno() <= last_ack_sent_) {
                        /*
                         * this is the case where the ts value is newer than
                         * the last one we've seen, and the seq # is the one
                         * we expect [seqno == last_ack_sent_] or older
                         */
                        recent_age_ = now();
                        recent_ = tcph->ts();
                }

                //
                // generate a stream of ecnecho bits until we see a true
                // cong_action bit
                //
                if (ecn_) {
                        if (fh->ce() && fh->ect()) {
                                // no CWR from peer yet... arrange to
                                // keep sending ECNECHO
                                recent_ce_ = TRUE;
                        } else if (fh->cwr()) {
                                // got CWR response from peer.. stop
                                // sending ECNECHO bits
                                recent_ce_ = FALSE;
                        }
                }

                // Header predication basically looks to see
                // if the incoming packet is an expected pure ACK
                // or an expected data segment

                if (datalen == 0) {
                        // check for a received pure ACK in the correct range..
                        // also checks to see if we are wnd_ limited
                        // (we don't change cwnd at all below), plus
                        // not being in fast recovery and not a partial ack.
                        // If we are in fast
                        // recovery, go below so we can remember to deflate
                        // the window if we need to
                        if (ackno > highest_ack_ && ackno < maxseq_ &&
                            cwnd_ >= wnd_ && !fastrecov_) {
                                newack(pkt);    // update timers,  highest_ack_
                                send_much(0, REASON_NORMAL, maxburst_);
                                Packet::free(pkt);
                                return;
                        }
                } else if (ackno == highest_ack_ && rq_.empty()) {
                        // check for pure incoming segment
                        // the next data segment we're awaiting, and
                        // that there's nothing sitting in the reassem-
                        // bly queue
                        //      give to "application" here
                        //      note: DELACK is inspected only by
                        //      tcp_fasttimo() in real tcp.  Every 200 ms
                        //      this routine scans all tcpcb's looking for
                        //      DELACK segments and when it finds them
                        //      changes DELACK to ACKNOW and calls tcp_output()
                        rcv_nxt_ += datalen;
                        flags_ |= TF_DELACK;
                        recvBytes(datalen); // notify application of "delivery"
                        //
                        // special code here to simulate the operation
                        // of a receiver who always consumes data,
                        // resulting in a call to tcp_output
                        Packet::free(pkt);
                        if (need_send())
                                send_much(1, REASON_NORMAL, maxburst_);
                        return;
                }
        } /* header prediction */


        //
        // header prediction failed
        // (e.g. pure ACK out of valid range, SACK present, etc)...
        // do slow path processing

        //
        // the following switch does special things for these states:
        //      TCPS_LISTEN, TCPS_SYN_SENT
        //

        switch (state_) {

        /*
         * If the segment contains an ACK then it is bad and do reset.
         * If it does not contain a SYN then it is not interesting; drop it.
         * Otherwise initialize tp->rcv_nxt, and tp->irs, iss is already
         * selected, and send a segment:
         *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
         * Initialize tp->snd_nxt to tp->iss.
         * Enter SYN_RECEIVED state, and process any other fields of this
         * segment in this state.
         */

        case TCPS_LISTEN:       /* awaiting peer's SYN */

                if (tiflags & TH_ACK) {
                        fprintf(stderr,
                                "%f: FullTcpAgent(%s): warning: recv'd ACK while in LISTEN: ",
                                now(), name());
                        prpkt(pkt);
                        // don't want ACKs in LISTEN
                        goto dropwithreset;
                }
                if ((tiflags & TH_SYN) == 0) {
                        fprintf(stderr,
                                "%f: FullTcpAgent(%s): warning: recv'd NON-SYN while in LISTEN\n",
                                now(), name());
                        prpkt(pkt);
                        // any non-SYN is discarded
                        goto drop;
                }

                /*
                 * must by a SYN (no ACK) at this point...
                 * in real tcp we would bump the iss counter here also
                 */
                dooptions(pkt);
                irs_ = tcph->seqno();
                t_seqno_ = iss_; /* tcp_sendseqinit() macro in real tcp */
                rcv_nxt_ = rcvseqinit(irs_, datalen);
                flags_ |= TF_ACKNOW;

                // check for a ECN-SYN with ECE|CWR
                if (ecn_ && fh->ecnecho() && fh->cong_action()) {

                        ect_ = TRUE;
                }


                if (fid_ == 0) {
                        // XXX: sort of hack... If we do not
                        // have a special flow ID, pick up that
                        // of the sender (active opener)
                        hdr_ip* iph = hdr_ip::access(pkt);
                        fid_ = iph->flowid();
                }

                newstate(TCPS_SYN_RECEIVED);
                goto trimthenstep6;

        /*
         * If the state is SYN_SENT:
         *      if seg contains an ACK, but not for our SYN, drop the input.
         *      if seg does not contain SYN, then drop it.
         * Otherwise this is an acceptable SYN segment
         *      initialize tp->rcv_nxt and tp->irs
         *      if seg contains ack then advance tp->snd_una
         *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
         *      arrange for segment to be acked (eventually)
         *      continue processing rest of data/controls, beginning with URG
         */

        case TCPS_SYN_SENT:     /* we sent SYN, expecting SYN+ACK (or SYN) */

                /* drop if it's a SYN+ACK and the ack field is bad */
                if ((tiflags & TH_ACK) &&
                        ((ackno <= iss_) || (ackno > maxseq_))) {
                        // not an ACK for our SYN, discard
                        fprintf(stderr,
                            "%f: FullTcpAgent::recv(%s): bad ACK for our SYN: ",
                                now(), name());
                        prpkt(pkt);
                        goto dropwithreset;
                }

                if ((tiflags & TH_SYN) == 0) {
                        fprintf(stderr,
                            "%f: FullTcpAgent::recv(%s): no SYN for our SYN: ",
                                now(), name());
                        prpkt(pkt);
                        goto drop;
                }

                /* looks like an ok SYN or SYN+ACK */
#ifdef notdef
cancel_rtx_timer();     // cancel timer on our 1st SYN [does this belong!?]
#endif
                irs_ = tcph->seqno();   // get initial recv'd seq #
                rcv_nxt_ = rcvseqinit(irs_, datalen);

                if (tiflags & TH_ACK) {
                        // SYN+ACK (our SYN was acked)
                        // CHECKME
                        // Check ECN-SYN+ACK packet
                        if (ecn_ && fh->ecnecho() && !fh->cong_action())
                                ect_ = TRUE;
                        highest_ack_ = ackno;
                        cwnd_ = initial_window();

#ifdef notdef
/*
 * if we didn't have to retransmit the SYN,
 * use its rtt as our initial srtt & rtt var.
 */
if (t_rtt_) {
        double tao = now() - tcph->ts();
        rtt_update(tao);
}
#endif

                        /*
                         * if there's data, delay ACK; if there's also a FIN
                         * ACKNOW will be turned on later.
                         */
                        if (datalen > 0) {
                                flags_ |= TF_DELACK;    // data there: wait
                        } else {
                                flags_ |= TF_ACKNOW;    // ACK peer's SYN
                        }

                        /*
                         * Received <SYN,ACK> in SYN_SENT[*] state.
                         * Transitions:
                         *      SYN_SENT  --> ESTABLISHED
                         *      SYN_SENT* --> FIN_WAIT_1
                         */

                        if (flags_ & TF_NEEDFIN) {
                                newstate(TCPS_FIN_WAIT_1);
                                flags_ &= ~TF_NEEDFIN;
                                tiflags &= ~TH_SYN;
                        } else {
                                newstate(TCPS_ESTABLISHED);
                        }

                        // special to ns:
                        //  generate pure ACK here.
                        //  this simulates the ordinary connection establishment
                        //  where the ACK of the peer's SYN+ACK contains
                        //  no data.  This is typically caused by the way
                        //  the connect() socket call works in which the
                        //  entire 3-way handshake occurs prior to the app
                        //  being able to issue a write() [which actually
                        //  causes the segment to be sent].
                        sendpacket(t_seqno_, rcv_nxt_, TH_ACK, 0, 0);
                } else {
                        // Check ECN-SYN packet
                        if (ecn_ && fh->ecnecho() && fh->cong_action())
                                ect_ = TRUE;

                        // SYN (no ACK) (simultaneous active opens)
                        flags_ |= TF_ACKNOW;
                        cancel_rtx_timer();
                        newstate(TCPS_SYN_RECEIVED);
                        /*
                         * decrement t_seqno_: we are sending a
                         * 2nd SYN (this time in the form of a
                         * SYN+ACK, so t_seqno_ will have been
                         * advanced to 2... reduce this
                         */
                        t_seqno_--;     // CHECKME
                }

trimthenstep6:
                /*
                 * advance the seq# to correspond to first data byte
                 */
                tcph->seqno()++;

                if (tiflags & TH_ACK)
                        goto process_ACK;

                goto step6;

        case TCPS_LAST_ACK:
        case TCPS_CLOSING:
                break;
        } /* end switch(state_) */

        /*
         * States other than LISTEN or SYN_SENT.
         * First check timestamp, if present.
         * Then check that at least some bytes of segment are within
         * receive window.  If segment begins before rcv_nxt,
         * drop leading data (and SYN); if nothing left, just ack.
         *
         * RFC 1323 PAWS: If we have a timestamp reply on this segment
         * and it's less than ts_recent, drop it.
         */

        if (ts_option_ && !fh->no_ts_ && recent_ && tcph->ts() < recent_) {
                if ((now() - recent_age_) > TCP_PAWS_IDLE) {
                        /*
                         * this is basically impossible in the simulator,
                         * but here it is...
                         */
                        /*
                         * Invalidate ts_recent.  If this segment updates
                         * ts_recent, the age will be reset later and ts_recent
                         * will get a valid value.  If it does not, setting
                         * ts_recent to zero will at least satisfy the
                         * requirement that zero be placed in the timestamp
                         * echo reply when ts_recent isn't valid.  The
                         * age isn't reset until we get a valid ts_recent
                         * because we don't want out-of-order segments to be
                         * dropped when ts_recent is old.
                         */
                        recent_ = 0.0;
                } else {
                        fprintf(stderr, "%f: FullTcpAgent(%s): dropped pkt due to bad ts\n",
                                now(), name());
                        goto dropafterack;
                }
        }

        // check for redundant data at head/tail of segment
        //      note that the 4.4bsd [Net/3] code has
        //      a bug here which can cause us to ignore the
        //      perfectly good ACKs on duplicate segments.  The
        //      fix is described in (Stevens, Vol2, p. 959-960).
        //      This code is based on that correction.
        //
        // In addition, it has a modification so that duplicate segments
        // with dup acks don't trigger a fast retransmit when dupseg_fix_
        // is enabled.
        //
        // Yet one more modification: make sure that if the received
        //      segment had datalen=0 and wasn't a SYN or FIN that
        //      we don't turn on the ACKNOW status bit.  If we were to
        //      allow ACKNOW to be turned on, normal pure ACKs that happen
        //      to have seq #s below rcv_nxt can trigger an ACK war by
        //      forcing us to ACK the pure ACKs
        //
        // Update: if we have a dataless FIN, don't really want to
        // do anything with it.  In particular, would like to
        // avoid ACKing an incoming FIN+ACK while in CLOSING
        //
        todrop = rcv_nxt_ - tcph->seqno();  // how much overlap?

        if (todrop > 0 && ((tiflags & (TH_SYN)) || datalen > 0)) {
//printf("%f(%s): trim 1..todrop:%d, dlen:%d\n",now(), name(), todrop, datalen);
                if (tiflags & TH_SYN) {
                        tiflags &= ~TH_SYN;
                        tcph->seqno()++;
                        th->size()--;   // XXX Must decrease packet size too!!
                                        // Q: Why?.. this is only a SYN
                        todrop--;
                }
                //
                // see Stevens, vol 2, p. 960 for this check;
                // this check is to see if we are dropping
                // more than this segment (i.e. the whole pkt + a FIN),
                // or just the whole packet (no FIN)
                //
                if ((todrop > datalen) ||
                    (todrop == datalen && ((tiflags & TH_FIN) == 0))) {
//printf("%f(%s): trim 2..todrop:%d, dlen:%d\n",now(), name(), todrop, datalen);
                        /*
                         * Any valid FIN must be to the left of the window.
                         * At this point the FIN must be a duplicate or out
                         * of sequence; drop it.
                         */

                        tiflags &= ~TH_FIN;

                        /*
                         * Send an ACK to resynchronize and drop any data.
                         * But keep on processing for RST or ACK.
                         */

                        flags_ |= TF_ACKNOW;
                        todrop = datalen;
                        dupseg = TRUE;  // *completely* duplicate

                }

                /*
                 * Trim duplicate data from the front of the packet
                 */

                tcph->seqno() += todrop;
                th->size() -= todrop;   // XXX Must decrease size too!!
                                        // why? [kf]..prob when put in RQ
                datalen -= todrop;

        } /* data trim */

        /*
         * If we are doing timstamps and this packet has one, and
         * If last ACK falls within this segment's sequence numbers,
         * record the timestamp.
         * See RFC1323 (now RFC1323 bis)
         */
        if (ts_option_ && !fh->no_ts_ && tcph->seqno() <= last_ack_sent_) {
                /*
                 * this is the case where the ts value is newer than
                 * the last one we've seen, and the seq # is the one we expect
                 * [seqno == last_ack_sent_] or older
                 */
                recent_age_ = now();
                recent_ = tcph->ts();
        }

        if (tiflags & TH_SYN) {
                fprintf(stderr,
                    "%f: FullTcpAgent::recv(%s) received unexpected SYN (state:%d): ",
                        now(), name(), state_);
                prpkt(pkt);
                goto dropwithreset;
        }

        if ((tiflags & TH_ACK) == 0) {
                fprintf(stderr, "%f: FullTcpAgent::recv(%s) got packet lacking ACK (state:%d): ",
                        now(), name(), state_);
                prpkt(pkt);
                goto drop;
        }

        /*
         * Ack processing.
         */

        switch (state_) {
        case TCPS_SYN_RECEIVED: /* want ACK for our SYN+ACK */
                if (ackno < highest_ack_ || ackno > maxseq_) {
                        // not in useful range
                        fprintf(stderr,
                                "%f: FullTcpAgent(%s): ack(%d) not in range while in SYN_RECEIVED: ",
                                now(), name(), ackno);
                        prpkt(pkt);
                        goto dropwithreset;
                }
                /*
                 * Make transitions:
                 *      SYN-RECEIVED  -> ESTABLISHED
                 *      SYN-RECEIVED* -> FIN-WAIT-1
                 */
                if (flags_ & TF_NEEDFIN) {
                        newstate(TCPS_FIN_WAIT_1);
                        flags_ &= ~TF_NEEDFIN;
                } else {
                        newstate(TCPS_ESTABLISHED);
                }
                cwnd_ = initial_window();
                /* fall into ... */

        /*
         * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
         * ACKs.  If the ack is in the range
         *      tp->snd_una < ti->ti_ack <= tp->snd_max
         * then advance tp->snd_una to ti->ti_ack and drop
         * data from the retransmission queue.
         *
         * note that state TIME_WAIT isn't used
         * in the simulator
         */

        case TCPS_ESTABLISHED:
        case TCPS_FIN_WAIT_1:
        case TCPS_FIN_WAIT_2:
        case TCPS_CLOSE_WAIT:
        case TCPS_CLOSING:
        case TCPS_LAST_ACK:

                //
                // look for ECNs in ACKs, react as necessary
                //

                if (fh->ecnecho() && (!ecn_ || !ect_)) {
                        fprintf(stderr,
                            "%f: FullTcp(%s): warning, recvd ecnecho but I am not ECN capable!\n",
                                now(), name());
                }

                //
                // generate a stream of ecnecho bits until we see a true
                // cong_action bit
                // 
                if (ecn_) {
                        if (fh->ce() && fh->ect())
                                recent_ce_ = TRUE;
                        else if (fh->cwr())
                                recent_ce_ = FALSE;
                }

                //
                // If ESTABLISHED or starting to close, process SACKS
                //

                if (state_ >= TCPS_ESTABLISHED && tcph->sa_length() > 0) {
                        process_sack(tcph);
                }

                //
                // ACK indicates packet left the network
                //      try not to be fooled by data
                //

                if (fastrecov_ && (datalen == 0 || ackno > highest_ack_))
                        pipe_ -= maxseg_;

                // look for dup ACKs (dup ack numbers, no data)
                //
                // do fast retransmit/recovery if at/past thresh
                if (ackno <= highest_ack_) {
                        // a pure ACK which doesn't advance highest_ack_
                        if (datalen == 0 && (!dupseg_fix_ || !dupseg)) {

                                /*
                                 * If we have outstanding data
                                 * this is a completely
                                 * duplicate ack,
                                 * the ack is the biggest we've
                                 * seen and we've seen exactly our rexmt
                                 * threshhold of them, assume a packet
                                 * has been dropped and retransmit it.
                                 *
                                 * We know we're losing at the current
                                 * window size so do congestion avoidance.
                                 *
                                 * Dup acks mean that packets have left the
                                 * network (they're now cached at the receiver)
                                 * so bump cwnd by the amount in the receiver
                                 * to keep a constant cwnd packets in the
                                 * network.
                                 */

                                if ((rtx_timer_.status() != TIMER_PENDING) ||
                                    ackno < highest_ack_) {
                                        // Q: significance of timer not pending?
                                        // ACK below highest_ack_
                                        oldack();
                                } else if (++dupacks_ == tcprexmtthresh_) {
                                        // ACK at highest_ack_ AND meets threshold
                                        //trace_event("FAST_RECOVERY");

                                        dupack_action(); // maybe fast rexmt
                                        goto drop;

                                } else if (dupacks_ > tcprexmtthresh_) {
                                        // ACK at highest_ack_ AND above threshole
                                        //trace_event("FAST_RECOVERY");
                                        extra_ack();

                                        // send whatever window allows
                                        send_much(0, REASON_DUPACK, maxburst_);
                                        goto drop;
                                }
                        } else {
                                // non zero-length [dataful] segment
                                // with a dup ack (normal for dataful segs)
                                // (or window changed in real TCP).
                                if (dupack_reset_) {
                                        dupacks_ = 0;
                                        fastrecov_ = FALSE;
                                }
                        }
                        break;  /* take us to "step6" */
                } /* end of dup/old acks */

                /*
                 * we've finished the fast retransmit/recovery period
                 * (i.e. received an ACK which advances highest_ack_)
                 * The ACK may be "good" or "partial"
                 */

process_ACK:

                if (ackno > maxseq_) {
                        // ack more than we sent(!?)
                        fprintf(stderr,
                            "%f: FullTcpAgent::recv(%s) too-big ACK (maxseq:%d): ",
                                now(), name(), int(maxseq_));
                        prpkt(pkt);
                        goto dropafterack;
                }

                /*
                 * If we have a timestamp reply, update smoothed
                 * round trip time.  If no timestamp is present but
                 * transmit timer is running and timed sequence
                 * number was acked, update smoothed round trip time.
                 * Since we now have an rtt measurement, cancel the
                 * timer backoff (cf., Phil Karn's retransmit alg.).
                 * Recompute the initial retransmit timer.
                 *
                 * If all outstanding data is acked, stop retransmit
                 * If there is more data to be acked, restart retransmit
                 * timer, using current (possibly backed-off) value.
                 */
                newack(pkt);    // handle timers, update highest_ack_

                /*
                 * if this is a partial ACK, invoke whatever we should
                 * note that newack() must be called before the action
                 * functions, as some of them depend on side-effects
                 * of newack()
                 */

                int partial = pack(pkt);

                if (partial)
                        pack_action(pkt);
                else
                        ack_action(pkt);

                /*
                 * if this is an ACK with an ECN indication, handle this
                 * but not if it is a syn packet
                 */

                if (fh->ecnecho() && !(tiflags&TH_SYN) )
                if (fh->ecnecho()) {
                        // Note from Sally: In one-way TCP,
                        // ecn() is called before newack()...
                        ecn(highest_ack_);  // updated by newack(), above
                        // "set_rtx_timer();" from T. Kelly.
                        if (cwnd_ < 1)
                                set_rtx_timer();
                }
                // CHECKME: handling of rtx timer
                if (ackno == maxseq_) {
                        needoutput = TRUE;
                }

                /*
                 * If no data (only SYN) was ACK'd,
                 *    skip rest of ACK processing.
                 */
                if (ackno == (highest_ack_ + 1))
                        goto step6;

                // if we are delaying initial cwnd growth (probably due to
                // large initial windows), then only open cwnd if data has
                // been received
                // Q: check when this happens
                /*
                 * When new data is acked, open the congestion window.
                 * If the window gives us less than ssthresh packets
                 * in flight, open exponentially (maxseg per packet).
                 * Otherwise open about linearly: maxseg per window
                 * (maxseg^2 / cwnd per packet).
                 */
                if ((!delay_growth_ || (rcv_nxt_ > 0)) &&
                    last_state_ == TCPS_ESTABLISHED) {
                        if (!partial || open_cwnd_on_pack_)
                          if (!ect_ || !hdr_flags::access(pkt)->ecnecho())
                                opencwnd();
                }

                if ((state_ >= TCPS_FIN_WAIT_1) && (ackno == maxseq_)) {
                        ourfinisacked = TRUE;
                }

                //
                // special additional processing when our state
                // is one of the closing states:
                //      FIN_WAIT_1, CLOSING, LAST_ACK

                switch (state_) {
                /*
                 * In FIN_WAIT_1 STATE in addition to the processing
                 * for the ESTABLISHED state if our FIN is now acknowledged
                 * then enter FIN_WAIT_2.
                 */
                case TCPS_FIN_WAIT_1:   /* doing active close */
                        if (ourfinisacked) {
                                // got the ACK, now await incoming FIN
                                newstate(TCPS_FIN_WAIT_2);
                                cancel_timers();
                                needoutput = FALSE;
                        }
                        break;

                /*
                 * In CLOSING STATE in addition to the processing for
                 * the ESTABLISHED state if the ACK acknowledges our FIN
                 * then enter the TIME-WAIT state, otherwise ignore
                 * the segment.
                 */
                case TCPS_CLOSING:      /* simultaneous active close */;
                        if (ourfinisacked) {
                                newstate(TCPS_CLOSED);
                                cancel_timers();
                        }
                        break;
                /*
                 * In LAST_ACK, we may still be waiting for data to drain
                 * and/or to be acked, as well as for the ack of our FIN.
                 * If our FIN is now acknowledged,
                 * enter the closed state and return.
                 */
                case TCPS_LAST_ACK:     /* passive close */
                        // K: added state change here
                        if (ourfinisacked) {
                                newstate(TCPS_CLOSED);
                                finish(); // cancels timers, erc
                                reset(); // for connection re-use (bug fix from ns-users list)
                                goto drop;
                        } else {
                                // should be a FIN we've seen
                                fprintf(stderr,
                                "%f: FullTcpAgent(%s)::received non-ACK (state:%d): ",
                                        now(), name(), state_);
                                prpkt(pkt);
                        }
                        break;

                /* no case for TIME_WAIT in simulator */
                }  // inner state_ switch (closing states)
        } // outer state_ switch (ack processing)

step6:

        /*
         * Processing of incoming DATAful segments.
         *      Code above has already trimmed redundant data.
         *
         * real TCP handles window updates and URG data here also
         */

/* dodata: this label is in the "real" code.. here only for reference */

        if ((datalen > 0 || (tiflags & TH_FIN)) &&
            TCPS_HAVERCVDFIN(state_) == 0) {

                //
                // the following 'if' implements the "real" TCP
                // TCP_REASS macro
                //

                if (tcph->seqno() == rcv_nxt_ && rq_.empty()) {
                        // got the in-order packet we were looking
                        // for, nobody is in the reassembly queue,
                        // so this is the common case...
                        // note: in "real" TCP we must also be in
                        // ESTABLISHED state to come here, because
                        // data arriving before ESTABLISHED is
                        // queued in the reassembly queue.  Since we
                        // don't really have a process anyhow, just
                        // accept the data here as-is (i.e. don't
                        // require being in ESTABLISHED state)
                        flags_ |= TF_DELACK;
                        rcv_nxt_ += datalen;
                        tiflags = tcph->flags() & TH_FIN;

                        // give to "application" here
                        // in "real" TCP, this is sbappend() + sorwakeup()
                        if (datalen)
                                recvBytes(datalen); // notify app. of "delivery"
                        needoutput = need_send();
                } else {
                        // see the "tcp_reass" function:
                        // not the one we want next (or it
                        // is but there's stuff on the reass queue);
                        // do whatever we need to do for out-of-order
                        // segments or hole-fills.  Also,
                        // send an ACK (or SACK) to the other side right now.
                        // Note that we may have just a FIN here (datalen = 0)
                        int rcv_nxt_old_ = rcv_nxt_; // notify app. if changes
                        tiflags = reass(pkt);
                        if (rcv_nxt_ > rcv_nxt_old_) {
                                // if rcv_nxt_ has advanced, must have
                                // been a hole fill.  In this case, there
                                // is something to give to application
                                recvBytes(rcv_nxt_ - rcv_nxt_old_);
                        }
                        flags_ |= TF_ACKNOW;

                        if (tiflags & TH_PUSH) {
                                //
                                // ???: does this belong here
                                // K: APPLICATION recv
                                needoutput = need_send();
                        }
                }
        } else {
                /*
                 * we're closing down or this is a pure ACK that
                 * wasn't handled by the header prediction part above
                 * (e.g. because cwnd < wnd)
                 */
                // K: this is deleted
                tiflags &= ~TH_FIN;
        }

        /*
         * if FIN is received, ACK the FIN
         * (let user know if we could do so)
         */

        if (tiflags & TH_FIN) {
                if (TCPS_HAVERCVDFIN(state_) == 0) {
                        flags_ |= TF_ACKNOW;
                        rcv_nxt_++;
                }
                switch (state_) {
                /*
                 * In SYN_RECEIVED and ESTABLISHED STATES
                 * enter the CLOSE_WAIT state.
                 * (passive close)
                 */
                case TCPS_SYN_RECEIVED:
                case TCPS_ESTABLISHED:
                        newstate(TCPS_CLOSE_WAIT);
                        break;

                /*
                 * If still in FIN_WAIT_1 STATE FIN has not been acked so
                 * enter the CLOSING state.
                 * (simultaneous close)
                 */
                case TCPS_FIN_WAIT_1:
                        newstate(TCPS_CLOSING);
                        break;
                /*
                 * In FIN_WAIT_2 state enter the TIME_WAIT state,
                 * starting the time-wait timer, turning off the other
                 * standard timers.
                 * (in the simulator, just go to CLOSED)
                 * (completion of active close)
                 */
                case TCPS_FIN_WAIT_2:
                        newstate(TCPS_CLOSED);
                        cancel_timers();
                        break;
                }
        } /* end of if FIN bit on */

        if (needoutput || (flags_ & TF_ACKNOW))
                send_much(1, REASON_NORMAL, maxburst_);
        else if (curseq_ >= highest_ack_ || infinite_send_)
                send_much(0, REASON_NORMAL, maxburst_);
        // K: which state to return to when nothing left?

        if (!halfclose_ && state_ == TCPS_CLOSE_WAIT && highest_ack_ == maxseq_)
                usrclosed();

        Packet::free(pkt);

        // haoboy: Is here the place for done{} of active close? 
        // It cannot be put in the switch above because we might need to do
        // send_much() (an ACK)
        if (state_ == TCPS_CLOSED) 
                Tcl::instance().evalf("%s done", this->name());

        return;

        //
        // various ways of dropping (some also ACK, some also RST)
        //

dropafterack:
        flags_ |= TF_ACKNOW;
        send_much(1, REASON_NORMAL, maxburst_);
        goto drop;

dropwithreset:
        /* we should be sending an RST here, but can't in simulator */
        if (tiflags & TH_ACK) {
                sendpacket(ackno, 0, 0x0, 0, REASON_NORMAL);
        } else {
                int ack = tcph->seqno() + datalen;
                if (tiflags & TH_SYN)
                        ack--;
                sendpacket(0, ack, TH_ACK, 0, REASON_NORMAL);
        }
drop:
        Packet::free(pkt);
        return;
}
/*  
 * Dupack-action: what to do on a DUP ACK.  After the initial check
 * of 'recover' below, this function implements the following truth
 * table:
 *  
 *      bugfix  ecn     last-cwnd == ecn        action  
 *  
 *      0       0       0                       full_reno_action
 *      0       0       1                       full_reno_action [impossible]
 *      0       1       0                       full_reno_action
 *      0       1       1                       1/2 window, return 
 *      1       0       0                       nothing 
 *      1       0       1                       nothing         [impossible]
 *      1       1       0                       nothing 
 *      1       1       1                       1/2 window, return
 */ 
    
void
FullTcpAgent::dupack_action()
{   

        int recovered = (highest_ack_ > recover_);

        fastrecov_ = TRUE;
        rtxbytes_ = 0;

        if (recovered || (!bug_fix_ && !ecn_) ||
            // Q: is last_cwnd_action == dupack enough to trigger?
            // probably not.  may need to fix 1-way reno model as well
            last_cwnd_action_ == CWND_ACTION_DUPACK) {
                goto full_reno_action;
        }       
    
        if (ecn_ && last_cwnd_action_ == CWND_ACTION_ECN) {
                slowdown(CLOSE_CWND_HALF);
                cancel_rtx_timer();
                rtt_active_ = FALSE;
                (void)fast_retransmit(highest_ack_);
                return; 
        }      
    
        if (bug_fix_) {
                /*
                 * The line below, for "bug_fix_" true, avoids
                 * problems with multiple fast retransmits in one
                 * window of data.
                 */      
                return;  
        }
    
full_reno_action:    
        slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_HALF);
        cancel_rtx_timer();
        rtt_active_ = FALSE;
        recover_ = maxseq_;
        (void)fast_retransmit(highest_ack_);
        // we measure cwnd in packets,
        // so don't scale by maxseg_
        // as real TCP does
        cwnd_ = double(ssthresh_) + double(dupacks_);
        return;
}

void
FullTcpAgent::timeout_action()
{
        recover_ = maxseq_;

        if (cwnd_ < 1.0) {
            fprintf(stderr,
            "%f: FullTcpAgent(%s):: resetting cwnd from %f to 1\n",
                 now(), name(), double(cwnd_));
                cwnd_ = 1.0;
        }

        if (last_cwnd_action_ == CWND_ACTION_ECN) {
                slowdown(CLOSE_CWND_ONE);
        } else {
                slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_RESTART);
                last_cwnd_action_ = CWND_ACTION_TIMEOUT;
        }
        reset_rtx_timer(1);
        t_seqno_ = (highest_ack_ < 0) ? iss_ : int(highest_ack_);
        fastrecov_ = FALSE;
        dupacks_ = 0;
}
/*
 * deal with timers going off.
 * 2 types for now:
 *      retransmission timer (rtx_timer_)
 *  delayed ack timer (delack_timer_)
 *      delayed send (randomization) timer (delsnd_timer_)
 *
 * real TCP initializes the RTO as 6 sec
 *      (A + 2D, where A=0, D=3), [Stevens p. 305]
 * and thereafter uses
 *      (A + 4D, where A and D are dynamic estimates)
 *
 * note that in the simulator t_srtt_, t_rttvar_ and t_rtt_
 * are all measured in 'tcp_tick_'-second units
 */

void
FullTcpAgent::timeout(int tno)
{

        if (state_ == TCPS_CLOSED || state_ == TCPS_LISTEN) {
                // shouldn't be getting timeouts here
                fprintf(stderr, "%f: FullTcpAgent(%s): unexpected timeout %d in state %s\n",
                        now(), name(), tno, statestr(state_));
                return;
        }

        switch (tno) {

        case TCP_TIMER_RTX:
                /* retransmit timer */
                ++nrexmit_;
                timeout_action();
                /* fall thru */
        case TCP_TIMER_DELSND:
                /* for phase effects */
                send_much(1, PF_TIMEOUT, maxburst_);
                break;

        case TCP_TIMER_DELACK:
                if (flags_ & TF_DELACK) {
                        flags_ &= ~TF_DELACK;
                        flags_ |= TF_ACKNOW;
                        send_much(1, REASON_NORMAL, 0);
                }
                delack_timer_.resched(delack_interval_);
                break;
        default:
                fprintf(stderr, "%f: FullTcpAgent(%s) Unknown Timeout type %d\n",
                        now(), name(), tno);
        }
        return;
}

void
FullTcpAgent::dooptions(Packet* pkt)
{
        // interesting options: timestamps (here),
        //      CC, CCNEW, CCECHO (future work perhaps?)

        hdr_flags *fh = hdr_flags::access(pkt);
        hdr_tcp *tcph = hdr_tcp::access(pkt);

        if (ts_option_ && !fh->no_ts_) {
                if (tcph->ts() < 0.0) {
                        fprintf(stderr,
                            "%f: FullTcpAgent(%s) warning: ts_option enabled in this TCP, but appears to be disabled in peer\n",
                                now(), name());
                } else if (tcph->flags() & TH_SYN) {
                        flags_ |= TF_RCVD_TSTMP;
                        recent_ = tcph->ts();
                        recent_age_ = now();
                }
        }

        return;
}

//
// this shouldn't ever happen
//
void
FullTcpAgent::process_sack(hdr_tcp*)
{
        fprintf(stderr, "%f: FullTcpAgent(%s) Non-SACK capable FullTcpAgent received a SACK\n",
                now(), name());
        return;
}


/*
 * ****** Tahoe ******
 *
 * for TCP Tahoe, we force a slow-start as the dup ack
 * action.  Also, no window inflation due to multiple dup
 * acks.  The latter is arranged by setting reno_fastrecov_
 * false [which is performed by the Tcl init function for Tahoe in
 * ns-default.tcl].
 */

/* 
 * Tahoe
 * Dupack-action: what to do on a DUP ACK.  After the initial check
 * of 'recover' below, this function implements the following truth
 * table:
 * 
 *      bugfix  ecn     last-cwnd == ecn        action  
 * 
 *      0       0       0                       full_tahoe_action
 *      0       0       1                       full_tahoe_action [impossible]
 *      0       1       0                       full_tahoe_action
 *      0       1       1                       1/2 window, return
 *      1       0       0                       nothing 
 *      1       0       1                       nothing         [impossible]
 *      1       1       0                       nothing 
 *      1       1       1                       1/2 window, return
 */

void
TahoeFullTcpAgent::dupack_action()
{  
        int recovered = (highest_ack_ > recover_);

        fastrecov_ = TRUE;
        rtxbytes_ = 0;

        if (recovered || (!bug_fix_ && !ecn_) ||
            // Q: is last_cwnd_action dupack enough?
            last_cwnd_action_ == CWND_ACTION_DUPACK) {
                goto full_tahoe_action;
        }
   
        if (ecn_ && last_cwnd_action_ == CWND_ACTION_ECN) {
                // slow start on ECN
                last_cwnd_action_ = CWND_ACTION_DUPACK;
                slowdown(CLOSE_CWND_ONE);
                set_rtx_timer();
                rtt_active_ = FALSE;
                t_seqno_ = highest_ack_;
                return; 
        }
   
        if (bug_fix_) {
                /*
                 * The line below, for "bug_fix_" true, avoids
                 * problems with multiple fast retransmits in one
                 * window of data.
                 */      
                return;  
        }
   
full_tahoe_action:
        // slow-start and reset ssthresh
        trace_event("FAST_RETX");
        recover_ = maxseq_;
        last_cwnd_action_ = CWND_ACTION_DUPACK;
        slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_ONE);   // cwnd->1
        set_rtx_timer();
        rtt_active_ = FALSE;
        t_seqno_ = highest_ack_;
        send_much(0, REASON_NORMAL, 0);
        return; 
}  

/*
 * ****** Newreno ******
 *
 * for NewReno, a partial ACK does not exit fast recovery,
 * and does not reset the dup ACK counter (which might trigger fast
 * retransmits we don't want).  In addition, the number of packets
 * sent in response to an ACK is limited to recov_maxburst_ during
 * recovery periods.
 */

NewRenoFullTcpAgent::NewRenoFullTcpAgent() : save_maxburst_(-1)
{
        bind("recov_maxburst_", &recov_maxburst_);
}

void
NewRenoFullTcpAgent::pack_action(Packet*)
{
        (void)fast_retransmit(highest_ack_);
        cwnd_ = double(ssthresh_);
        if (save_maxburst_ < 0) {
                save_maxburst_ = maxburst_;
                maxburst_ = recov_maxburst_;
        }
        return;
}

void
NewRenoFullTcpAgent::ack_action(Packet* p)
{
        if (save_maxburst_ >= 0) {
                maxburst_ = save_maxburst_;
                save_maxburst_ = -1;
        }
        FullTcpAgent::ack_action(p);
        return;
}

/*
 *
 * ****** SACK ******
 *
 * for Sack, receiver part must report SACK data
 * sender part maintains a 'scoreboard' (sq_) that
 * records what it hears from receiver
 * sender fills holes during recovery and obeys
 * "pipe" style control until recovery is complete
 */

void
SackFullTcpAgent::reset()
{
        sq_.clear();                    // no SACK blocks
        sack_min_ = h_seqno_ -1;        // no left edge of SACK blocks
        FullTcpAgent::reset();
}


int
SackFullTcpAgent::hdrsize(int nsackblocks)
{
        int total = FullTcpAgent::headersize();
        // use base header size plus SACK option size
        if (nsackblocks > 0) {
                total += ((nsackblocks * sack_block_size_)
                        + sack_option_size_);
        }
        return (total);
}

void
SackFullTcpAgent::dupack_action()
{

        int recovered = (highest_ack_ > recover_);

        fastrecov_ = TRUE;
        rtxbytes_ = 0;
        pipe_ = maxseq_ - highest_ack_ - sq_.total();

//printf("%f: SACK DUPACK-ACTION:pipe_:%d, sq-total:%d, bugfix:%d, cwnd:%d, highest_ack:%d, recover_:%d\n",
//now(), pipe_, sq_.total(), bug_fix_, int(cwnd_), int(highest_ack_), recover_);

        if (recovered || (!bug_fix_ && !ecn_)) {
                goto full_sack_action;
        }           

        if (ecn_ && last_cwnd_action_ == CWND_ACTION_ECN) {
                last_cwnd_action_ = CWND_ACTION_DUPACK;
                cancel_rtx_timer();
                rtt_active_ = FALSE;
                send_much(1, REASON_DUPACK, maxburst_);
                return; 
        }               
   
        if (bug_fix_) {
                /*                              
                 * The line below, for "bug_fix_" true, avoids
                 * problems with multiple fast retransmits in one
                 * window of data.
                 */      

//printf("%f: SACK DUPACK-ACTION BUGFIX RETURN:pipe_:%d, sq-total:%d, bugfix:%d, cwnd:%d\n",
//now(), pipe_, sq_.total(), bug_fix_, int(cwnd_));
                return;  
        }
   
full_sack_action:                               
        trace_event("FAST_RECOVERY");
        slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_HALF);
        cancel_rtx_timer();
        rtt_active_ = FALSE;

        // these initiate SACK-style "pipe" recovery
        pipectrl_ = TRUE;
        recover_ = maxseq_;     // where I am when recovery starts

        int amt = fast_retransmit(highest_ack_);
        h_seqno_ = highest_ack_ + amt;

//printf("%f: FAST-RTX seq:%d, h_seqno_ is now:%d, pipe:%d, cwnd:%d, recover:%d\n",
//now(), int(highest_ack_), h_seqno_, pipe_, int(cwnd_), recover_);

        send_much(0, REASON_DUPACK, maxburst_);

        return;
}

void
SackFullTcpAgent::pack_action(Packet* p)
{
        if (!sq_.empty() && sack_min_ < highest_ack_) {
                sack_min_ = highest_ack_;
                sq_.cleartonxt();
        }
        pipe_ -= maxseg_;       // see comment in tcp-sack1.cc
        if (h_seqno_ < highest_ack_)
                h_seqno_ = highest_ack_;
}

void
SackFullTcpAgent::ack_action(Packet* p)
{
//printf("%f: EXITING fast recovery, recover:%d\n",
//now(), recover_);
        fastrecov_ = pipectrl_ = FALSE;
        if (!sq_.empty() && sack_min_ < highest_ack_) {
                sack_min_ = highest_ack_;
                sq_.cleartonxt();
        }
        dupacks_ = 0;
}

//
// receiver side: if there are things in the reassembly queue,
// build the appropriate SACK blocks to carry in the SACK
//
int
SackFullTcpAgent::build_options(hdr_tcp* tcph)
{
        int total = FullTcpAgent::build_options(tcph);

        if (!rq_.empty()) {
                int nblk = rq_.gensack(&tcph->sa_left(0), max_sack_blocks_);
                tcph->sa_length() = nblk;
                total += (nblk * sack_block_size_) + sack_option_size_;
        } else {
                tcph->sa_length() = 0;
        }
        return (total);
}

void
SackFullTcpAgent::timeout_action()
{
        FullTcpAgent::timeout_action();

        //
        // original SACK spec says the sender is
        // supposed to clear out its knowledge of what
        // the receiver has in the case of a timeout
        // (on the chance the receiver has renig'd).
        // Here, this happens when clear_on_timeout_ is
        // enabled.
        //

        if (clear_on_timeout_) {
                sq_.clear();
                sack_min_ = highest_ack_;
        }

        return;
}

void
SackFullTcpAgent::process_sack(hdr_tcp* tcph)
{
        //
        // Figure out how many sack blocks are
        // in the pkt.  Insert each block range
        // into the scoreboard
        //

        if (max_sack_blocks_ <= 0) {
                fprintf(stderr,
                    "%f: FullTcpAgent(%s) warning: received SACK block but I am not SACK enabled\n",
                        now(), name());
                return;
        }       

        int slen = tcph->sa_length(), i;
        for (i = 0; i < slen; ++i) {
                if (tcph->sa_left(i) >= tcph->sa_right(i)) {
                        fprintf(stderr,
                            "%f: FullTcpAgent(%s) warning: received illegal SACK block [%d,%d]\n",
                                now(), name(), tcph->sa_left(i), tcph->sa_right(i));
                        continue;
                }
                sq_.add(tcph->sa_left(i), tcph->sa_right(i), 0);  
        }

        return;
}

int
SackFullTcpAgent::send_allowed(int seq)
{
        // not in pipe control, so use regular control
        if (!pipectrl_)
                return (FullTcpAgent::send_allowed(seq));

        // don't overshoot receiver's advertised window
        int topawin = highest_ack_ + int(wnd_) * maxseg_;
        if (seq >= topawin) {
//printf("%f: SEND(%d) NOT ALLOWED DUE TO AWIN:%d, pipe:%d, cwnd:%d\n",
//now(), seq, topawin, pipe_, int(cwnd_));
                return FALSE;
        }

        // don't overshoot cwnd_
        int cwin = int(cwnd_) * maxseg_;
        return (pipe_ < cwin);
}


//
// Calculate the next seq# to send by send_much.  If we are recovering and
// we have learned about data cached at the receiver via a SACK,
// we may want something other than new data (t_seqno)
//

int
SackFullTcpAgent::nxt_tseq()
{

        int in_recovery = (highest_ack_ < recover_);
        int seq = h_seqno_;

        if (!in_recovery) {
//if (int(t_seqno_) > 1)
//printf("%f: non-recovery nxt_tseq called w/t_seqno:%d\n",
//now(), int(t_seqno_));
//sq_.dumplist();
                return (t_seqno_);
        }

        int fcnt;       // following count-- the
                        // count field in the block
                        // after the seq# we are about
                        // to send
        int fbytes;     // fcnt in bytes

//if (int(t_seqno_) > 1)
//printf("%f: recovery nxt_tseq called w/t_seqno:%d, seq:%d, mode:%d\n",
//now(), int(t_seqno_), seq, sack_rtx_threshmode_);
//sq_.dumplist();

        while ((seq = sq_.nexthole(seq, fcnt, fbytes)) > 0) {
                // if we have a following block
                // with a large enough count
                // we should use the seq# we get
                // from nexthole()
                if (sack_rtx_threshmode_ == 0 ||
                    (sack_rtx_threshmode_ == 1 && fcnt >= sack_rtx_cthresh_) ||
                    (sack_rtx_threshmode_ == 2 && fbytes >= sack_rtx_bthresh_) ||
                    (sack_rtx_threshmode_ == 3 && (fcnt >= sack_rtx_cthresh_ || fbytes >= sack_rtx_bthresh_)) ||
                    (sack_rtx_threshmode_ == 4 && (fcnt >= sack_rtx_cthresh_ && fbytes >= sack_rtx_bthresh_))) {

//if (int(t_seqno_) > 1)
//printf("%f: nxt_tseq<hole> returning %d\n",
//now(), int(seq));
                        // adjust h_seqno, as we may have
                        // been "jumped ahead" by learning
                        // about a filled hole
                        if (seq > h_seqno_)
                                h_seqno_ = seq;
                        return (seq);
                } else if (fcnt <= 0)
                        break;
                else {
                        seq += maxseg_;
                }
        }
//if (int(t_seqno_) > 1)
//printf("%f: nxt_tseq<top> returning %d\n",
//now(), int(t_seqno_));
        return (t_seqno_);
}

---